linux-kernel - Re: [PATCH 3/3] iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked

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Message-ID: <20240522124517.GB69273@ziepe.ca>
Date: Wed, 22 May 2024 09:45:17 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Uros Bizjak <ubizjak@...il.com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 3/3] iommufd: Use atomic_long_try_cmpxchg() in
 incr_user_locked_vm()

On Wed, May 22, 2024 at 10:26:49AM +0200, Uros Bizjak wrote:
> Use atomic_long_try_cmpxchg() instead of
> atomic_long_cmpxchg (*ptr, old, new) != old in incr_user_locked_vm().
> cmpxchg returns success in ZF flag, so this change saves a compare
> after cmpxchg (and related move instruction in front of cmpxchg).
> 
> Also, atomic_long_try_cmpxchg() implicitly assigns old *ptr
> value to "old" when cmpxchg fails. There is no need to re-read
> the value in the loop.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/iommufd/pages.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

This patch may as well go through Joerg's tree with the whole series

Thanks,
Jason